Prematurity and insufficient lung alveolar lining surfactant are closely related to neonatal Respiratory Distress Syndrome (RDS). Phosphatidylcholine (PC) is a particularly effective lung alveolar lining surfactant. PC of lung is normally stored in lamellar bodies and is then secreted to help line the air-alveolar interface to stabilize the lung and aid respiration. Phospholipids, including PC, can form multilamellar concentric bilayer vesicles with the lipid layers separated by aqueous medium (liposomes). When made together with cholesterol, liposomes can be used to introduce otherwise membrane-impermeable substances into cells. There is limited data showing that lung can take up liposomally entrapped substances, and to date there are no studies on attempting to deliver liposomal PC (PC in liposomal bilayer vesicles) to lung lamellar bodies. The objective of this research is to study the use of liposomal-PC to deliver PC to labellar body. This project will attempt 1) to show that C14-PC of liposomal bilayer vesicles is taken up by the lung, in vivo; 2) to establish the kinetics and optimun conditions of liposomal PC uptake by lamellar body by defining such factors as time, concentration, dose method, and liposomal charge and liposomal size.